Erosion resistant materials find use in many applications wherein surfaces are subject to eroding forces. For example, refinery process vessel walls and internals exposed to aggressive fluids containing hard, solid particles such as catalyst particles in various chemical and petroleum environments are subject to both erosion and corrosion. The combined properties of high temperature erosion resistance and toughness are required for linings and inserts used to provide long term erosion/abrasion resistance of internal metal surfaces in refining and petrochemical process units with operating temperatures above 600° F. The protection of these vessels and internals against erosion and corrosion induced material degradation especially at high temperatures is a technological challenge. Excellent erosion resistance is also required in certain oil & gas exploration and production equipment exposed to particularly abrasive materials, such as sand. Refractory liners are used currently for components requiring protection against the most severe erosion and corrosion such as the inside walls of internal cyclones used to separate solid particles from fluid streams, for instance, the internal cyclones in fluid catalytic cracking units (also referred to as “FCCU”) for separating catalyst particles from the process fluid.
The state-of-the-art in erosion resistant materials is chemically bonded castable alumina refractories. The castable alumina refractories have adequate temperature and corrosion resistance, but limited erosion resistance. These castable alumina refractories are applied to the surfaces in need of protection and upon heat curing hardens and adheres to the surface via metal-anchors or metal-reinforcements. It also readily bonds to other refractory surfaces so as to provide either a patch or a full lining. The typical chemical composition of one commercially available refractory is 80.0% Al2O3, 7.2% SiO2, 1.0% Fe2O3, 4.8% MgO/CaO, 4.5% P2O5 in wt %. The life span of the state-of-the-art refractory liners is significantly limited by excessive mechanical attrition of the liner from the high velocity solid particle impingement, mechanical cracking and spallation. Exemplary solid particles are catalyst and coke. The primary erosion mechanism is cracking of the phosphate bond phase through the binder phase as shown in the cross sectional scanning electron micrograph of FIG. 1 depicting a prior art standard refractory sample used in the refinery and petrochemical process applications subjected to high temperature erosion under simulated FCCU service conditions. Cracks in the binder phase are clearly apparent in the micrograph. When these bonds are upgraded with stronger direct bonding of the ceramic grains, the overall lining becomes expensive to fabricate and prone to catastrophic, brittle fracture failures.
Thin layer ceramic coatings or weld overlays of precipitation hardened alloy may also be used for high temperature erosion resistance, but are less effective than conventional chemically bonded, castable refractory linings. Thickness and ceramic content are constrained in weld overlays and plasma sprayed coatings because the layer is applied in a molten form over a solid based metal and residual thermal/forming stresses are limiting.
Harder ceramic materials also tend to be too brittle and their lack of toughness adversely affects unit reliability. Metal rich ceramic-metal composites, such as hard facing, may alternatively be used but fall short of the level of erosion resistance provided by the aforementioned castables because forming/fabrication techniques limit the amount of hard, coarse grained ceramics available in the microstructure. Metal matrix composites with a higher content of hard ceramic grains have been designed with superior erosion resistance and toughness via powder metallurgy techniques for applications less than 600° F., but the current art does not provide compositions with temperature and corrosion resistance usable for advantage in refining and petrochemical process applications.
The limited hot erosion resistance of state-of-the-art ceramic rich, ceramic-metal composites such as WC bonded with Co or Ni cemented carbides is attributed to the lack the thermodynamic stability for long term, high temperature wear/erosion applications in corrosive environments. As depicted in FIG. 2, these materials are reactive with oxygen at FCCU temperatures when compared to more refractory steel and ceramic grains (TiC, SS, FeCrAlY). On the other hand, precipitation hardened alloys have a stable composition in high temperature process environments, but lack the high concentrations of hard ceramics and/or the shape and sizing of the these aggregates to optimize protecting the less wear resistant metal binding component from erosion.
Linings and inserts are used in numerous high temperature refining and petrochemical processes to protect internal steel surfaces from erosion/abrasion caused by circulating particulate solids such as catalyst or coke. One such application is cyclone separators. Over the past decade, significant advances in the cyclone design and refractory lining materials led to dramatic improvements in the operability and efficiency of FCCU units. At the same time, however, demands on the cyclone systems have been increasing due to commercial incentives for longer run lengths, higher throughput velocities, improved separation efficiency, and the use of harder, low attrition catalysts. Thus, high temperature erosion resistance and lining durability continue to be material properties limiting the reliability and run length of the FCCUs today and materials with an improved combination of durability and erosion resistance would offer enhancements in unit performance.
A need exists for linings, inserts and coatings for use in refining and petrochemical processing applications that have a combination of improved erosion/corrosion resistance at high temperatures compared to the state of the art refractory and excellent fracture toughness while still maintaining equivalent or better thickness and attachment reliability as the state of the art refractory. A need also exists for linings, inserts and coatings for use in oil & gas exploration and production that have improved erosion resistance when exposed to abrasive solid particle environments.